Single-walled and multiwalled carbon nanotube blends with polyvinylidene difluoride (and its copolymers) have been characterized. The nanotubes are observed to form a well-dispersed, structurally random nanophase within the fluoropolymer matrix. X-ray analysis coupled with differential scanning calorimetry suggests that the nanophase alters crystal formation within the polymer. For most loadings and nanotube types, the piezoelectric β-polymorph is significantly enhanced over other crystal phases. Solution-cast composite thin films exhibit enhancements in both the pyroelectric response and mechanical transduction over pure polymer. This is interpreted as resulting from the change in crystallinity.

Properties of Polyvinylidene Difluoride−Carbon Nanotube Blends

Ferroelectric composites are now an established alternative to conventional ferroelectric ceramic materials and to the more recently discovered ferroelectric polymers. These materials due to their unique blending of polymetric properties of mechanical flexibility, formability and low cost with high electro-active properties have been been suggested to be a viable alternative both in piezoelectric and pyroelectric transducer applications. This review is devoted to the piezoelectric and pyroelectric properties exhibited by these type of composites with a special reference to those made of ceramic particles embedded in a polymer matrix (i.e. 0-3 connectivity type composite). A review of models predicting the electro-active properties of 0-3 composites is presented together with a proposal for a new mixed connectivity cubes model to be applicable to the case of high ceramic loading and/or when the ceramic grain size incorporated in the polymer matrix is comparable to the thickness of the sample. A review of the experimental results of the piezo- and pyroelectric properties of various ferroelectric composite materials, reported by several workers, is also presented in this paper. Special reference is made to composites made from calcium modified lead titanate and poly(vinyldene fluoride-trifluorethylene) emphasizing their advantages in the poling process which is a critical phase in the process of obtaining successful electro-active 0-3 composite electrets.

Inorganic ceramic/polymer ferroelectric composite electrets

The present work aims at the study of molecular relaxations in PVDF/BaTiO3 nanocomposites using broadband dielectric spectroscopy. The nanocomposites of PVDF with BaTiO3 (10–30% by wt%) are prepared using simple melt mixing method. In dielectric permittivity study, two relaxation processes are identified corresponding to the crystalline, glass transition in the PVDF/BaTiO3 nanocomposites. The peaks shift to higher frequencies as the temperature is increased. Electric modulus formalism is used to analyze the dielectric relaxations to overcome the conductivity effects at low frequencies. In M′′ spectra two peaks are observed only at high temperature and low frequency whereas a single relaxation peak appears at low temperatures. The single relaxation peak appearing at low temperatures is the αc relaxation attributed to crystalline chain relaxation in PVDF and the second relaxation peak which appears only at high temperatures and at a frequency lower than αc relaxation is identified as MWS relaxation. The temperature dependence of αc relaxation and MWS relaxation follows Arrhenius type behavior.

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Dielectric relaxations in PVDF/BaTiO3 nanocomposites

Smart materials, which exhibit piezoelectricity, find an eclectic range of applications in the industry. The direct piezoelectric effect has been widely used in sensor design, and the inverse piezoelectric effect has been applied in actuator design. Ever since 1954, PZT and BaTiO3 were widely used for sensor and actuator applications despite their toxicity, brittleness, inflexibility, etc. With the discovery of PVDF in 1969, followed by development of copolymers, a flexible, easy to process, nontoxic, high density alternate with high piezoelectric voltage coefficient was available. In the past 20 years, heterostructural materials like polymer ceramic composites, have received lot of attention, since these materials combine the excellent pyroelectric and piezoelectric properties of ceramics with the flexibility, processing facility, and strength of the polymers resulting in relatively high dielectric permittivity and breakdown strength, which are not attainable in a single phase piezoelectric material. The current review article is an attempt to provide a compendium of all the work carried out with reference to PVDF-PZT composites. The review article evaluates the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application. POLYM. ENG. SCI., 55:1589–1616, 2015. © 2015 Society of Plastics Engineers

Dielectric and piezoelectric properties of PVDF/PZT composites: A review

Composite technology, where a novel artificial material is fabricated by combining, for example, ceramic and polymer materials in an ordered manner or just by mixing, was earlier used widely for sonar, medical diagnostics, and NDT purposes. However, in recent decades, large numbers of ceramic–polymer composites have been introduced for telecommunication and microelectronic applications. For these purposes, composites of 0–3 connectivity (a three-dimensionally connected polymer phase is loaded with isolated ceramic particles) are the most attractive from the application point of view. Composites of 0–3 connectivity enable flexible forms and very different shapes with very inexpensive fabrication methods including simply mixing and molding. In this brief review, we gather together the research carried out within 0–3 ceramic–polymer composites for microwave substrates, also including embedded capacitor, inductor, or microwave-absorbing performances.

Polymer–Ceramic Composites of 0–3 Connectivity for Circuits in Electronics: A Review

Composites of electroactive ceramics and ferroelectric polymers are important for applications since they combine the most important features of the both phases and their properties can be easily tailored to various requirements. As the dielectric permittivity is involved in figures of merit of the quantities important for applications we studied dielectric response of Pb(Zr 0.5 Ti 0.5 )O 3 –polyvinylidene fluoride nanocomposites over a wide frequency and temperature range. It was found that though the permittivity value of the composites is high due to the high permittivity of the ceramics, the glass transition of the polymer and dielectric relaxation related to the wide-angle oscillation of polar groups attached to the main polymer chain determine the dielectric behaviour of the composites.

Dielectric relaxation in ferroelectric PZT–PVDF nanocomposites

Electroactive composites based on ferroelectric ceramic and polymer components are still of interest since their properties can be easily tailored to the requirements of smart structures, sensors and actuators. We studied the dielectric and pyroelectric response of poly(vinylidene fluoride) loaded with BaTiO3 nanograins obtained by mechanically activated synthesis from BaO and TiO2. The BaTiO3 nanopowder was characterized by X-ray diffraction, transmission electron microscopy and NIR Raman scattering. The relaxation processes in the polymer matrix were found to determine the dielectric response of the composites but with higher permittivity values due to the presence of BaTiO3. The activation energy of the segmental motion of the polymer matrix was found to increase with increasing contents of the filler. The dielectric response of the composites with volumetric fraction of BaTiO3 equal to and greater than 0.24 was found to be dominated by a broad maximum at ∼320 K, which we relate to the Curie point of the ferroelectric nanograins.

Dielectric and pyroelectric response of PVDF loaded with BaTiO3 obtained by mechanosynthesis

Dielectric relaxation and pyroelectric response of the barium titanate–poly (vinyl chloride) BaTiO3–PVC composites of 0–3 connectivity and volume fraction of ceramics ϕ from 0.0 to 0.4 were investigated. Dielectric properties of the composites were found to be a combination of those of pure PVC polymer and BaTiO3 ceramics: the value of dielectric permittivity increases with increasing volume fraction of the ceramics but the temperature dependence is determined by two relaxation processes in the polymer (at ∼270 K – the local motion of the small groups in the chain and at ∼350 K – the segmental molecular motion) and in the ceramics (dielectric anomaly at the phase transitions). The value of the pyroelectric coefficient p of poled composites increases with ϕ and depends on the light modulation frequency fm as p ∼ f–nm with n ≈ 0.9 to 1.1, dependently on ϕ. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric and pyroelectric properties of BaTiO3–PVC composites

Dielectric response of (0–3) type composites, made of BaTiO 3 particles with mean size of 20–30 nm and polyvinylidene fluoride was found to be determined by the response of BaTiO 3 with a broad Cur...

Dielectric and Pyroelectric Response of BaTiO3-PVDF Nanocomposites

The influence of thermal aging on the resonance frequency and electric impedance of polyvinylidenefluoride (PVDF) type polymer films was studied with the aim to apply thermal treatment to modify and tune the parameters of polymer electromechanical transducers. Results of our study show that thermal treatment of PVDF/TRFE 75/25 copolymer in the temperature range 50 to 125/spl deg/C (10 min) can be applied for matching the resonance frequencies of coupled transducers. The resonance frequency of the copolymer was found to increase linearly with the rise of the annealing temperature by /spl sim/12%, whereas the related decrease in the electromechanical coupling coefficient does not exceed /spl sim/11%.

J. Kulek

Papers

Dielectric relaxation in ferroelectric PZT–PVDF nanocomposites

Dielectric and pyroelectric response of PVDF loaded with BaTiO3 obtained by mechanosynthesis

Dielectric and pyroelectric properties of BaTiO3–PVC composites

Dielectric and Pyroelectric Response of BaTiO3-PVDF Nanocomposites

The method of matching resonance frequencies in coupled transmitter PVDF/TRFE diaphragms